Re: [Jfs-discussion] [PATCH v2 27/28] ext4: xattr inode deduplication

2017-06-02 Thread Darrick J. Wong
On Fri, Jun 02, 2017 at 05:46:22AM -0700, Tahsin Erdogan wrote:
> > Hmm... normally we'd supply sbi->s_csum_seed as the second argument so
> > that the metadata checksum value also has the fs uuid stamped into it.
> 
> I have thought about using sbi->s_csum_seed and was a little hesitant
> because it involves adding more complexity to e2fsprogs to handle
> cases like changing uuid or turning off metadata_csum. After thinking
> more about this, I think it is doable.

e2fsprogs already has code to walk the fs to rewrite/remove checksums,
so it shouldn't be too much effort to tap into that to rewrite the
ea_info hash.

> > Even if you dismiss that, we usually follow the convention of
> > initializing the crc32c calculation with (~0U), not (0U), to strengthen
> > crc32c's ability to detect zeroes being injected at the start of the
> > stream.
> 
> Agreed, using ~0 is definitely better than 0.

--D

--
Check out the vibrant tech community on one of the world's most
engaging tech sites, Slashdot.org! http://sdm.link/slashdot
___
Jfs-discussion mailing list
Jfs-discussion@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/jfs-discussion


Re: [Jfs-discussion] [PATCH v2 27/28] ext4: xattr inode deduplication

2017-06-02 Thread Tahsin Erdogan
> Hmm... normally we'd supply sbi->s_csum_seed as the second argument so
> that the metadata checksum value also has the fs uuid stamped into it.

I have thought about using sbi->s_csum_seed and was a little hesitant
because it involves adding more complexity to e2fsprogs to handle
cases like changing uuid or turning off metadata_csum. After thinking
more about this, I think it is doable.

> Even if you dismiss that, we usually follow the convention of
> initializing the crc32c calculation with (~0U), not (0U), to strengthen
> crc32c's ability to detect zeroes being injected at the start of the
> stream.

Agreed, using ~0 is definitely better than 0.

--
Check out the vibrant tech community on one of the world's most
engaging tech sites, Slashdot.org! http://sdm.link/slashdot
___
Jfs-discussion mailing list
Jfs-discussion@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/jfs-discussion